Anderson localization of composite excitations in disordered optomechanical arrays
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00:00
Phased arrayComposite materialSchwache LokalisationWhiteParticle physicsPlain bearingVideoYearPaperElectronSchwache LokalisationRRS DiscoveryMembrane potentialGround stationCrystallizationCrystal structureMode of transportWind waveMental disorderBulk modulusQuantumHot workingCylinder blockConvertibleComputer animation
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Interference (wave propagation)
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FACTS (newspaper)Hot workingAutomobile platformSchwache LokalisationPanel painting
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Phased arrayAudio frequencyCouchTypesettingScale (map)Optical cavityRadiation pressurePhotonicsColorfulnessRear-view mirrorMechanicSemiconductor device fabricationViseSchwache LokalisationCell (biology)Audio frequencyArray data structureEnergy levelRadioactive decaySeparation processPhononBand gapHybrid rocketEngine displacementField strengthQuantumCrystallizationAutomobile platformLaserMembrane potentialGroup delay and phase delayMode of transportAngeregter ZustandOpticsCylinder blockEffects unitDisc brakeLaserFuelStationeryMultiplizitätPhotographyAtmospheric pressurePhotonHourFACTS (newspaper)Transfer functionPair productionRing strainFunkgerätWeightJuneComputer animation
Transcript: English(auto-generated)
00:03
It's well known since the early years of quantum mechanics that the normal modes of systems with crystal symmetry are block waves which extend to the whole bulk of the crystal. For more than 30 years after the discovery of quantum mechanics, the extended nature
00:21
of the normal modes was thought to be just a generic consequence of the phenomenon of tunneling, and thus a robust feature in the presence of disorder. This commonly held view was refuted by Phil Anderson in a paper published in 1958. In this paper, he demonstrated that the randomness of the potential can convert extended wave
00:44
functions to localized ones, a phenomenon now known as Anderson localization. While Anderson's work focused on electrons, Anderson localization is a generic, undulatory phenomenon. More specifically, it's an interference phenomenon. As such, it can be suspended by
01:03
dephasing. For this reason, its reliable identification in solid-state samples is a real experimental challenge. Therefore, any new platform which allows one to detect and to explore localization is of great importance. In this work, we study Anderson localization in an array of optomechanical systems. Let
01:27
us first briefly review the physics of the building block of our array, a standard optomechanical system comprising of a pair of optical and mechanical modes interacting via radiation pressure. The archetypal optomechanical system is a Fabry-Perot cavity with a movable
01:45
mirror driven by a laser. The photons inside the cavity are reflected by the movable mirror and thus transfer momentum to the mirror. On the other hand, the displacement of the movable mirror changes the cavity length and thus its optical eigenfrequencies.
02:03
We note that the optomechanical interaction, while very weak at the level of a single photon, is nonlinear and thus can be enhanced and tuned by the laser light. That's why optomechanical systems are so versatile and can be deployed for a wide range of tasks,
02:22
including precise sensing, quantum information processing, and tests of quantum behavior at a large scale. Next, let us see how to build an array of optomechanical systems. An array of Fabry-Perot cavities would not be a very practical solution. Fortunately, there are a few optomechanical platforms which are very promising
02:45
in terms of scalability. An example of a scalable platform is based on optomechanical microdisks. The first small-scale optomechanical array of this type has been recently demonstrated by the group of Michal Lipson. Even a greater potential for scalability is offered by
03:05
optomechanical crystals. The relevant interactions in a 1D array are sketched in the ladder diagram. Photons and phonons can hop between neighboring cells. In addition, on each side, photons can be converted into phonons and vice versa. This interaction is mediated
03:25
by an appropriately tuned laser. Most importantly, due to fabrication imperfections, the optical and mechanical frequencies of individual optomechanical cells are disordered, leading to the physics of Anderson localization investigated in our article.
03:44
The effects of localization in our peculiar setting can be visualized by plotting the local density of states as a function of energy, the y-axis, and side, the x-axis. The color scale ranges from orange to blue as the excitations type ranges from phononics
04:04
to photonics. It is also instructive to inspect the individual wave functions. The particular wave function shown here reveals a separation of length scales associated to different exponential decays and thus localization lengths. We also investigate the localization
04:24
length more systematically for different strengths of the optomechanical interaction. This reveals a complex behavior that crucially depends on the hybridization and the presence of an interaction-induced gap in the density of states. These complex features represent
04:42
unequivocal footprints of the phenomenon of Anderson localization and are robust in the presence of this patient.